An oligomerization reaction is usually carried out as a homogenous catalytic process in the presence of metallorganic catalysts. The output stream of an oligomerization reactor usually is a mixture of olefin oligomers, namely, reaction products, an initial olefin, a catalyst and/or residues thereof and often a solvent. In order to separate reaction products, various methods are used in this field of the art. For example, Russian patent No. 2131405 describes a method of isolating products of a trimerization reaction of olefins, said products being obtained by means of a catalyst comprising chromium compounds and organoaluminum compounds; the method comprising contacting a reaction product stream from the outlet of a reactor with an alcohol, in the course of which a catalyst system is deactivated. After that, the olefin product is separated, and a residue is contacted with an aqueous base, thereby forming a chromium-containing solid sediment. Then, the solid sediment, an aqueous layer and an organic layer are separated with subsequent addition of a mineral acid to an aqueous phase. A drawback of the method is the presence of an alcohol in the reaction mixture, which can result in the residues of this alcohol ending up in an olefin product and in a recurrent solvent if it is used, which, in turn, leads to impairing of the quality thereof. In addition, heavy olefin products can be contaminated with this alcohol during the treatment hereof with an acid. Furthermore, the use of the indicated method results in the complication of the scheme and the control system of the process because it is necessary to thoroughly control a proportion of alcohol and/or amine, to add firstly the alkaline solution before adding the acidic solution, and to separate the precipitated sediment.
Russian patent No. 2249585 mentions another drawback of the aforesaid method, namely, the isolation of hydrogen halide in the presence of alkyl-aluminum halides in the catalyst system. Therefore, the solution is further improved by adding an amine, instead of an alcohol or in addition to an alcohol, to bind a released hydrogen halide. However, this entails an additional complication of the scheme and the necessity to utilize/isolate residues of the amine or a salt thereof.
U.S. Pat. No. 5,750,816 describes the solution that is closest to the proposed one, said solution optionally includes addition of alcohol, amine, phenol, carboxylic acid and other compounds for the maintenance of the catalyst components in a dissolved state. At the same time, the use of these components is not obligatory. In order to simplify the scheme, a by-product polymer that is usually formed in a trimerization reaction is not separated from the reaction product stream before a distillation column, wherein the separation of the reaction products and a solvent when used from residues of the catalyst and the by-product polymer isolated in the solid state is carried out. At the same time, the content of the column botton is heated to a temperature of 200° C. or more to separate high-boiling reaction products. It is noted that the preliminary separation of the polymer before the distillation step in this method results in the sedimentation of the catalyst residues in the form of a resin on the surface of a heater and in impairing the operation thereof. A drawback of this method is the formation of a solid residue after the distillation, said residue comprising by-product polymer and catalyst residues, and it is difficult to utilize said residue because a fine-dispersed polymer contaminated with the catalyst residues is capable of holding a significant amount of substances comprised in the catalyst residues, due to adsorption and/or absorption. This hampers their isolation by conventional methods such as the treatment with acidic or alkaline, aqueous or organic solution. Furthermore, the presence of a dispersed by-product polymer in the stream of products from the reactor to the distillation column requires the maintenance of an increased temperature or other methods making it possible to avoid the sedimentation of a polymer in the line and in apparatuses which are present in the production line, including measuring devices.
The problem to be solved within the scope of the present invention is an isolation of products of an oligomerization reaction of olefins comprising a terminal double bond, from the output stream of an oligomerization reactor, and a separation of a polymeric by-product and catalyst residues, including aluminum and chromium compounds.
In order to solve the problem, a method is provided that does not comprise adding any agents to deactivate a catalyst system, wherein the method consists in isolation of products of an oligomerization reaction of olefins comprising a terminal double bond, said reaction being conducted by the action of a catalyst comprising chromium compounds, a nitrogen-containing ligand and organoaluminum compounds, said method comprising the following three sequential steps:
a) isolating at least one liquid product of the oligomerization reaction of olefins from an output stream of an oligomerization reactor;
b) treating a residue with an aqueous solution of an acid; and
c) separating an organic layer and an aqueous layer.
The problem is solved by a method that does not comprise adding any agents for deactivating a catalyst system. The method comprises the step of separating a by-product polymer from the output stream of an oligomerization reactor before feeding the stream into a distillation column. The distillation is carried out stepwise, at first isolating at least one olefin reaction product. In order to avoid the formation of a resin during the distillation of high-boiling reaction products after the step of separating at least one olefin, a mixture that is formed after the separation and comprises the high-boiling reaction products, is treated with an aqueous solution of an acid to separate catalyst residues, first of all aluminum and chromium compounds, in the form of water-soluble salts, with subsequent separation of aqueous and organic phases. Then, the organic phase may be fed to the next distillation step to isolate high-boiling products.
Firstly, the use of the proposed methods allows the isolation of target reaction products, avoiding the ingress of impurities of foreign substances, such as alcohols into products and/or recurrent solvent, and elimination of the necessity of the separation of these foreign substances. Secondly, the use of the proposed method makes it possible to avoid the contamination of lines and devices between the reactor and the distillation column with a side product. Thirdly, the solution makes it possible to separate catalyst residues from a polymer by-product, thus facilitating the regeneration of the catalyst or separation of metal compounds from catalyst residues, while avoiding the precipitation of a resin during the distillation of the high-boiling reaction products. Thus, the proposed solution makes it possible to achieve results exceeding or at least comparable with earlier known methods, and avoiding drawbacks inherent herein.